Reconfiguration of the Noaa Topaz Lidar for Ground-based Measurement of Ozone and Aerosol Backscatter

The NOAA Tunable Optical Profiler for Aerosol and oZone (TOPAZ) lidar is a differential absorption lidar (DIAL) for measuring ozone concentration and aerosol backscatter profiles that was originally designed for nadir-looking operation from an airborne platform. In order to expand the capabilities of this system, we have reconfigured the TOPAZ system for ground-based zenith-looking operation and have constructed an optical scanner to allow measurements at low pointing angles (0-30 degrees). In this new configuration, TOPAZ is capable of making measurements from ground level to several kilometers altitude with high vertical resolution near the ground. The (reversibly) reconfigured system has been installed in a truck and was deployed to the Uintah Basin Winter Ozone Study (UBWOS) experiment in eastern Utah, USA. The TOPAZ lidar modifications and the new scanner are described, and data acquired in this new configuration are presented. 1. BRIEF LIDAR DESCRIPTION The NOAA TOPAZ lidar [1], [2] is designed around an all solid state Ce:LiCAF-based laser which is tunable from 285-310 nm. The system is operated with three output wavelengths tuned sequentially on a pulse-topulse basis to provide the signals needed for a DIAL measurement of ozone profiles along with aerosol backscatter profiles. The pulses are ~100 ns wide, the pulse rate is 1000 Hz, and the combined output of the three wavelengths is ~100 mW. The laser beam is transmitted coaxially with the receiver telescope. The receiver portion of the lidar uses a 0.5 m diameter telescope to collect the backscattered light and photomultiplier tubes for detection in two channels (near-field and far-field). The signals from these two channels are digitized and accumulated in a custom field programmable gate array (FPGA)-based data acquisition system. The digitized signals are then saved to disk and processed using a first-cut analysis for realtime display to the lidar operators. An iterative DIAL analysis technique was developed for this system to calculate the ozone and aerosol profiles and to remove effects on the ozone profiles due to differential aerosol backscatter and extinction. In its airborne (nadir-looking) configuration, TOPAZ is capable of measuring ozone with 90-m and 10-s resolution along the lidar line-of-sight with <5% typical and up to 15% accuracy [2] depending on the total atmospheric attenuation along the measurement path. Uncalibrated aerosol backscatter profiles are measured with 18-m resolution for the same 10-s interval. For both measurements, the profiles start ~400 m from the lidar (limited by transmitter-to-receiver overlap) and can extend up to 5000 m range. Significantly more details of the airborne configuration of the TOPAZ lidar and the analysis of its signals may be found in [1] and [2]. 2. RECONFIGURATION FOR GROUND-